Abstract:The effects of solid solution and aging treatments on the microstructural evolution and hardness of the GWZ932 alloy in the rolled state were investigated by means of optical microscope, X-ray diffractometer, Vickers hardness tester, scanning electron microscope, transmission electron microscope, and high-angle annular dark-field scanning transmission electron microscope. The results show that the alloy microstructure in the rolled state mainly consists of α-Mg, massive 18R-LPSO phase, lamellar 14H-LPSO phase, rare-earth-rich phase and Zn-Zr phase. The lamellar 14H-LPSO is almost completely dissolved into the matrix by solid solution treatment at 500 ℃ for 2 h; the elongated acicular 14H-LPSO is precipitated from the α-Mg matrix after 4 h of solid solution, and its volume fraction gradually increases with the extension of time; the volume fraction of acicular 14H-LPSO reaches 16% after 6 h of solid solution; the acicular 14H-LPSO phase dissolves and re-precipitates the lamellar 14H-LPSO (about 14.9 μm in length and 8.2 μm in width), and a small amount of undissolved acicular 14H-LPSO phase grows to form rod-like 14H-LPSO (23.4 μm in length and 1.98 μm in width). Increasing the solid solution temperature to 520 ℃, the solute atom diffusion rate is accelerated, thus the complete dissolution and re-precipitation time of lamellar 14H-LPSO is advanced to 1 and 2 h, respectively, and the size of the re-precipitated lamellar 14H-LPSO phase (12.6 μm in length, 5.1 μm in width) is smaller than that of the re-precipitated one after solid solution at 500 ℃ for 8 h. Precipitation and transformation do not occur during solid solution treatment at 520 ℃, indicating that the precipitation and dissolution of the acicular 14H-LPSO phase and its content are affected by the solid solution temperature and time. The age-hardening curves reach peak hardness under conditions of 520 ℃, 4 h+225 ℃, 64 h. On this basis, the age-hardening behaviour of the alloy after solution treatment at 520 ℃ for 4 h was investigated and the results show that the alloy reaches peak hardness after age treatment at 225 ℃ for 64 h. The room-temperature tensile strength (UTS), yield strength (YS) and elongation (EL) of the alloy under peak aging conditions are 396.3 MPa, 274 MPa, and 12.7% increase by 23.8%, 7.4%, and 69.3%, compared to those of the rolled state, respectively. The excellent strength and plasticity of the alloys arise from the precipitation of a columnar β'' phase (about 28.9 nm in length and 8.9 nm in width with an average area fraction of about 11.7%) and a basal 18R-LPSO/γ'' phase in the α-Mg matrix.